(a) Field
The described technology relates generally to a frame transmitting method and a frame receiving method. More particularly, the described technology relates generally to a frame transmitting method and a frame receiving method in a wireless local area network (WLAN).
(b) Description of the Related Art
A frequency band used in the WLAN is an unlicensed band, and other wireless devices, for example Bluetooth devices, besides WLAN devices can use the same frequency band. Therefore, the WLAN devices use a carrier sense multiple access (CSMA) protocol to avoid collisions with the other WLAN devices or the other wireless devices. In the CSMA protocol, the WLAN device detects energy on a channel and transmits the signal only when the channel is not being used. In this case, the WLAN device occupies the channel by transmitting a request to send (RTS) frame or a clear to send (CTS) frame. The other devices set a network allocation vector (NAV) based on a duration field of the RTS frame or CTS frame and do not perform the contention for a channel access during the NAV duration.
A current WLAN can a wide bandwidth by using a primary channel together with a second channel. For example, the IEEE standard 802.11ac may use bandwidths such as 20 MHz, 40 MHz, 80 MHz, and 160 MHz through a secondary channel of 20 MHz, a secondary channel of 40 MHz, and a secondary channel of 80 MHz as well as the primary channel of 20 MHz. However, the secondary channel should be always used together with the primary channel. Accordingly, even if the other device uses some bands including the primary channel, unoccupied channels cannot be used.
On the other hand, a basic service set (BSS) operating on the same channel as a device's BSS and within (either partly or wholly) its basic service area (BSA) may exist in the WLAN. This BSS is called an overlapping basic service set (OBSS). In the high density WLAN environment, if the OBSS uses the primary channel, unoccupied secondary channels cannot be used because of the NAV set by the OBSS.
As such, the current WLAN cannot efficiently use the channels.